Review on High-Performance MAHLE MS16340 Gasket: Engine Seal for Maximum Efficiency by Chad Cypert

The superior quality you expect from a Mahle brand. Very well made and made in the USA as an added bonus. If you don't want to buy GM factory seals, I think that's the only option. Most other aftermarket seals use red/orange rubber, which isn't great, and GM had a service bulletin updated to the green/turquoise that Mahle uses.